1. Field of the Invention
The present invention relates to an apparatus and method for measuring quality of sound encoded with a variable band multi-codec, and more particularly, to an apparatus and method for measuring quality of sound encoded with a variable band multi-codec, and determining the cause of sound quality deterioration when sound quality deteriorates, when a packet network provides multimedia services in real time in connection with an existing wired/wireless network.
This work was supported by the IT R&D program of MIC/IITA [2005-S-100-02, Development of Multi-codec and Its Control Technology Providing Variable bandwidth Scalability].
2. Description of the Related Art
In general, variable band multi-codecs are used to convert a natural sound into digital data having a variety of transmission rates.
For example, when a natural sound is encoded, frequency bands are divided into a narrow band (from 300 Hz to 3,400 Hz), a wide band (from 50 Hz to 7,000 Hz), and an audio band (from 20 Hz to 20,000 Hz), wherein each band can provide a transmission rate of 8, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 or 32 kbps. In a Voice over Internet Protocol (VoIP) telephone service through a packet network, it is assumed that bands provided through the packet network are variable and cannot be estimated. For above example, in the VoIP telephony service, a variable band multi-codec obtains the best sound quality at a transmission rate of 32 kbps, and obtains the worst sound quality at a transmission rate of 8 kps.
If packets can be transmitted with high sound quality due to the margin of the network band, packets will be transmitted at a transmission rate of 32 kbps. If the network environment becomes poor due to a change in the network band, packets will be transmitted at a transmission rate of 30 kbps. If the network environment becomes worse, packets will be transmitted at a transmission rate of 28 kbps, and if the network environment becomes further worse than the above case, packets will be transmitted at a transmission rate of 26 kbps. As such, in the variable band multi-codec, since a transmission rate depends on a network environment, sound quality can deteriorate. But data loss, delay, etc. will be reduced, because less problem is generated in data transmission over the network,
That is, in the variable band multi-codec, if the transmission rate is high, high sound quality is achieved but network transfer loss or delay increases, and if the transmission rate is low, sound quality deteriorates but the possibility of network transfer loss or delay being generated decreases.
In order to apply such a variable band multi-codec, a signal protocol transform technique for call set-up is used. The signal protocol transform technique is disclosed in RFC (Request for Comments) 3261 “SIP”, RFC 3264 “Offer/Answer SDP”, RFC 2833 “RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals”, RFC 2327 “SDP”, RFC 3108 “ATM SDP”, RFC 1890 “RTP Profile Payload type”, etc., issued by the Internet Engineering Task Force (IETF).
Meanwhile, in order to enhance Quality of Service (QoS) with respect to sound quality in the variable band multi-codec, it is necessary to control a transmission rate with respect to a required sound quality. That is, in the variable band multi-codec, sound quality must be measured in an end-to-end way so that data can be transmitted at a correct transmission rate.
A conventional end-to-end sound quality measurement method is described below.
Korean Laid-open Patent Application No. 2003-0019839 entitled “Detecting Device for Quality of Conversation in Mobile Communication System and Method Therefor”, which was laid-open on Mar. 7, 2003, discloses an apparatus for measuring sound quality in real time in a mobile communication system.
Also, Korean Laid-open Patent Application No. 2000-0025237 entitled “Method of Automatically Measuring Quality of Vocoder of CDMA System”, which was laid-open on May 6, 2000, discloses an apparatus for automatically measuring the quality of a vocoder installed in a control station of a CDMA system.
Also, U.S. Pat. No. 7,002,992 entitled “Codec Selection to Improve Media Communication”, which was published on Feb. 21, 2006, discloses an apparatus for selecting a codec according to network parameters.
Also, U.S. Pat. No. 5,657,420 entitled “Variable Rate Vocoder”, which was published on Aug. 12, 1997, discloses a codec standard for a vocoder having a variety of transmission rates, developed by Qualcomm Corporation.
However, the above-mentioned conventional techniques cannot recognize differences between objects that are to be subjected to end-to-end sound quality measurement, and cannot determine the cause of sound quality distortion. Accordingly, a method and apparatus for measuring quality of sound encoded with a variable band multi-codec in real time are need. And a method and apparatus for determining the cause of sound quality distortion are needed.